1. Field of the Invention
THE PRESENT INVENTION RELATES GENERALLY TO FINISHING MACHINES AND MORE PARTICULARLY TO A VIBRATORY FINISHING MACHINE OF THE CONTINUOUS FEED TYPE HAVING A DISCHARGE SYSTEM FOR CONTROLLING THE RETENTION TIME OF WORKPIECES WITHIN THE TUB OF THE MACHINE.
2. Prior Art
Vibratory finishing machines adapted to smooth and finish the surfaces of workpieces by such operations as deburring, burnishing, descaling, and cleaning are well known. Such machines commonly employ a movably mounted processing tub for receiving a quantity of workpieces and abrasive finishing media. A finishing action is imparted to the workpieces by vibrating the tub.
As brought out in the referenced patents, the abrasive media can conveniently be separated from the workpieces after the media and workpieces are discharged from the tub. After separation, the finishing media may then be returned to the tub of the finishing machine for reuse. The finishing liquid is usually drained off during separation of the media and workpieces. The finished workpieces may subsequently be conveyed to a separate unit of group of units for washing, drying, inspection and packaging.
Continuous feed vibratory finishing machines typically provide the processing tub with spaced charging and discharging devices whereby media and workpieces enter one end of the tub and are subjected to a finishing action as they progress through the tub for discharge at the opposite end.
One problem with a number of prior proposals for continuous feed vibratory finishing machines is that the time during which workpieces are retained in the tub is not readily controllable. Workpieces of a relatively soft metal, or workpieces needing only minimal deburring, etc., require only a short retention time. Workpieces of harder metal which have many large burrs to be removed, require longer retention times. Hence, where the retention time requirements differ from that provided by prior continuous feed finishing machines, it has previously been necessary to operate the finishing machine on a batch process basis where the retention time can be carefully controlled.
The machines described in the referenced Continuous Feed Patents are provided with discharge systems for controlling the retention time of workpieces in the tub of the machine. These machines may be operated on a batch basis if desired but are designed primarily for continuous operation according to a prearranged time schedule. Each of the machines has a discharge system including a closure-controlled discharge opening. One of the advantages of these machines is that the closure operating cycle can be adjusted by the operator from time to time to lengthen or shorten the retention time of materials within the tub. The discharge closure can be opened and closed by a timing control device preset to selected intervals of operation.
Once the closure operating cycle has been decided upon, the operator adjusts the timing mechanism to provide the predetermined retention period, typically about ten seconds, for processing the workpieces constituting part of the contents of the tub. This is normally followed by a release period--typically 5 seconds--for partial discharge of materials from the tub. This cycle of closure operation is continually repeated and establishes an effective rate of discharge of materials from the tub which determines the retention time of workpieces in the tub. In some cases, the nature of the workpieces may call for longer or shorter processing times than those mentioned above. In such instances, the operator can readily reset the timing mechanism to provide correspondingly longer or shorter retention periods.
In the operation of the machine, the charging apparatus supplies the tub as required with suitable abrasive processing media. An aqueous finishing liquid is usually introduced concurrently into the tub to facilitate finishing of the workpieces. The workpieces themselves are added by an operator. For all practical purposes, the operation of the charging apparatus is keyed to that of the discharge system and simply returns the abrasive media which has been discharged from the tub back into the tub.
A problem which is not addressed by the inventions of the Continuous Feed patents is that of materials which may occasionally become trapped in the region of the discharge opening between the closure and the sturcture which defines the discharge opening. This problem is of concern where the workpieces being finished can be damaged if trapped by the full force of the closure operator system. The problem can also cause excessive wear to parts of the finishing machine. A resilient liner on the closure, for example, can be caused to wear excessively by repetitive engagements with trapped materials. When discharge structure components are formed from plastic material such as molded polyurethane, they too can wear excessively when trapped materials are repetitively clamped against them.